Tradeoffs from a Real-World Climate Geoengineering Experience

The idea of "geoengineering" as a response to climate change involves putting particles, probably sulfur, into the atmosphere.

This aims to counterbalance the effects of carbon and other warming gases.

The idea is controversial. One side emphasizes the risks of tinkering with the climate; indeed, the 2013 movie Snowpiercer and the follow-up TV show envision a future where geoengineering to counterbalance global warming goes too far and leads to an ice age. On the other side, if you feel that the risks of climate change are immediate and enormous, and that attempts to reduce carbon emissions at a global level are not close to sufficient, then the logic of that position pushes you to consider alternatives that you might not otherwise prefer–from geoengineering to a renaissance of nuclear power, and others. (For some previous posts over the last decade or so on geoengineering, see here, here, here, and here.)

But just as increasing sulfur emissions into the atmosphere would be a form of geoengineering to push back against climate change risks, reducing sulfur emissions into the atmosphere will be a form of geoengineering that increases climate change risks. Back in 2020, the International Maritime Organization agreed to reduce sulfur emissions from shipping. The goal was to reduce conventional air pollutants related to sulfur in port cities, and from this perspective, the policy was a big success. But from the perspective of climate change, it may well have made the problem worse. Syris Valentine tells the story in a readable way, with links to the underlying scientific studies, in “How cleaning up shipping cut pollution — and warmed the planet,” subtitled “When the maritime sector slashed sulfur emissions, it became an accidental experiment in geoengineering” (Grist, July 18, 2024).

Sulfur emissions from maritime sources dropped 80%. Studies done before the program was adopted estimated that this reduction would save at least 500,000 lives during the next five years, mainly in port cities around the world that bear the brunt of these emissions.

On the other side, several studies also suggest that less sulfur in the atmosphere had led to shifts in cloud patterns that could double the amount of global warming over the next decade. For those who want details of the evidence, here’s a prominent study published in Atmospheric Chemistry and Physics, and another study published in Communications Earth and Environment. As one might expect in this area, the studies are not in full agreement: here’s a preprint, awaiting review, of a study that finds a smaller effect.

A group of seven researchers are concerned enough about this issue that they are publishing an open letter, forthcoming in a journal called Oxford Open Climate Change, asking the International Maritime Organization to alter its rules so that ships would continue to emit more sulfur when out on the open seas, away from population centers. The idea is to keep the immediate health benefits of lower sulfur emissions near port cities, but also keep sulfur in the air to counterbalance the warming effects of carbon emissions.

The practical tradeoff here is real, and so are the challenges of thinking about geoengineering. If you favor an immediate, do everything now, all-hands-on-deck approach to addressing risks of climate change, then continuing the previously existing form of geoengineering–in the form of having ships emitting sulfur while away from land–makes sense. If you are opposed to this form of geoengineering, even though this practice of ships putting sulfur into the atmosphere has existed for some decades, then you are also willing to accept that the need for reducing carbon concentrations in the atmosphere should be balanced against other environmental concerns.